文件操作（二进制读写）

/***
a.txt
***/
this is a word
helloworld

/***
file.c
***/
#include<stdio.h>
#include<stdlib.h>
#include<string.h>

int main()
{
    FILE *p = fopen("./a.txt","r");
    while(!feof(p))
    {
        char buf[100] = {0};
        fscanf(p,"%s",buf);
        printf("%s
",buf);
    }
    fclose(p);
    return 0;
}

fscanf()函数和scanf函数用法一样。fscanf是从一个文件中读取字符串，scanf是从键盘读取字符串。（遇到空格就停止）

/***
a.txt
***/
23 + 45 = 
35 + 63 =
34 + 45 =

/***
file1.txt
***/
#include<stdio.h>
#include<stdlib.h>
#include<string.h>

int main()
{
    int a,b;
    FILE *p = fopen("./a.txt","r");
    while(!feof(p))
    {
        char buf[100] = {0};
        //fgets(buf,"%s",p);
        //fscanf(p,"%s",buf);
        fscanf(p,"%d + %d = ",&a,&b);
        printf("a = %d , b = %d
",a,b);
        //printf("%s
",buf);
    }
    fclose(p);
    return 0;
}

/***
fprintf.c
***/
#include<stdio.h>
#include<string.h>

int main()
{
    FILE *p = fopen("./b.txt","w");
    char buf[100] = "hello world";
    fprintf(p,"%s",buf);
    fclose(p);
    return 0;
} 

fread()函数和fwrite()函数：操作文本文件和二进制文件

fopen()函数只能读文本文件

/***
fread.c
***/

#include<stdio.h>
int main()
{
    FILE *p = fopen("./a.txt","rb");
    char buf[100] = {0};
fread(buf,sizeof(char),1,p); //第一个参数是缓冲区，第二个参数是读取字节大小，第三个 //参数表示读取字节个数，第四个参数表示文件指针
    printf("buf = %s
",buf);
    fclose(p);
    return 0;
}

/***
fread1.c
***/

#include<stdio.h>
int main()
{
    FILE *p = fopen("./a.txt","rb");

    while(!feof(p))
    {
        char buf[20] = {0};
        fread(buf,sizeof(char),sizeof(buf),p);
        printf("buf = %s
",buf);
    }
    fclose(p);
    return 0;
}

fread()函数有返回值，返回的是size_t类型，unsigned int ==》 %u

/***
fread.c
***/
#include<stdio.h>
int main()
{
    FILE *p = fopen("./c.txt","rb");
    char buf[1024] = {0};
    size_t res = fread(buf,sizeof(char),sizeof(buf),p);
    printf("res = %u
",res);
/*
    while(!feof(p))
    {
        char buf[20] = {0};
        fread(buf,sizeof(char),sizeof(buf),p);
        printf("buf = %s
",buf);
    }
*/
    fclose(p);
    return 0;
}

/***
c.txt
***/
asd

运行结果：res = 4（文件结尾有一个换行字符‘ ’?）;

size_t res = fread(buf,sizeof(int),sizeof(buf),p);

运行结果：res = 1；

以上程序的运行结果和windos环境下读文本文件的结果会出现差异。

/***
fwrite.c
***/
#include<stdio.h>

int main()
{
    FILE *p = fopen("./d.txt","wb");
    char buf[1024] = {0};
    buf[0] = 'a';
    buf[1] = 'b';
    buf[2] = 'c';
    fwrite(buf,sizeof(char),sizeof(buf),p);
    fclose(p);
    return 0;
}

运行结果：abc

文件大小是1K（buf）数组大小，文件后面全是0。

/***
fwrite.c
***/
#include<stdio.h>

int main()
{
    FILE *p = fopen("./d.txt","w");
    int a = 0x12345678;
    fwrite(&a,sizeof(char),4,p);
    fclose(p);
    return 0;
}